1. Field of the Invention
This invention relates to a tape cassette and, more particularly to a tape cassette provided with a front lid which covers the front of the cassette housing and a spring member which by the spring action forces the front lid in its closing direction.
2. Description of the Prior Art
Tape cassettes provided with a front lid which covers the open front of the cassette housing and a spring member which by the spring action forces the front lid in its closing direction are in wide use. For ease of fitting such a spring member in a cassette housing, the spring member is first set in a front lid, and the spring-loaded lid is temporarily connected to an upper half casing of the housing. Meanwhile reels and other components are assembled in a lower half casing in advance. The upper casing with the front lid kept open against the action of the spring member is fitted to the lower casing and joined securely, and finally the front lid is released by the spring member to the closing position. Japanese Utility Model Kokoku No. 7-13109 proposes a design in which a pivot of a front lid is equipped with a coiled spring while an upper half casing is provided with a guide rib for guiding a free end of a spring member, so that a leg of the coiled spring is guided by the guide rib to facilitate the fitting of the spring means in place and preclude the possibility of the free end of the spring member being disengaged from its receiving part. FIGS. 6 and 7 illustrate two typical prior art structures and methods of assembling these components.
FIG. 6 depicts a conventional structure, (a) showing a front lid fitted to an upper casing, and (b) the front lid swung open to set the casing to a lower casing. The upper casing is then turned upside down and fitted to the lower casing. The procedure will now be explained in detail. The front lid 19 is generally L-shaped, consisting of a top strip 23 and a front strip 22, with sidewalls 24, 24 on both sides. The sidewalls 24 are formed in one piece with pivots 25, one for each. A coiled portion 33 of a spring member 20 is secured to one of the pivots 25, and a leg 34 of the spring member having a bend 26 at the end is hooked on the inside of the top strip 23 of the front lid 19. The upper casing 2 has retaining ribs for positioning the pivots 25, formed on the inner side (underside) of the front top wall 35 of the casing. Also a recess 36 is formed on the underside of the front top wall 35 to receive the leg at the free end of the spring member 20. The retaining ribs are adapted to be combined with corresponding retaining ribs of the lower casing to provide bearings for turnably supporting the pivots 25. When the front lid 19 thus fitted with the spring member 20 is to be set to the upper casing 2, the pivot 25 at the end where it is not loaded with the spring member 20 is first fitted to the upper casing 2. Next, the top wall 35 of the upper casing 2 is caused to slide into the space between the spring-loaded pivot 25 and the leg 34 at the free end of the spring member, and both pivots 25 are brought into contact with the retaining ribs. The leg 34 of the spring member 20 that had been caught in the top strip 23 is thus engaged with the recess 36 of the upper casing 2. The temporarily assembled state is shown in FIG. 6(a).
Next, the upper casing 2 with the front lid 19 attached is put on and joined with the lower casing (not shown; refer to the lower casing 1 in FIG. 1 according to the present invention) in which reels 14 and other components have been fitted in place. Prior to the joining, the front lid 19 has to be swung and kept in the open position shown in FIG. 6(b) to avoid its interference with the tape in the lower casing. At this point the pivots 25 are not secured yet, and the front end of the leg of the spring member 20 that has the bend 26 provided to prevent scratching and biting into the upper casing tends to slip out of place, causing the front lid to come off depending on the direction of external force applicable to the lid during the matching of the upper casing with the lower casing.
FIG. 7 illustrates another structure of the prior art in (a) and (b) which correspond, respectively, to (a) and (b) of FIG. 6. Here a spring member 20 has no bend formed at its free end 37. Unlike that of FIG. 6, this structure does not allow the front lid to come off during assembling. However, when the front lid is swung to the position as shown in FIG. 7(b) for connection to the lower casing, a pivot 25 yet to be secured in place rises, retracting the free end 37 of the spring member as in FIG. 7(b). After the upper casing has been matched with the lower casing, the free end of the spring member bites into the wall of a recess 36 formed in the underside (inner surface) of the upper wall of the upper casing 2 and fails to return to the original position. This can result in malfunction of the front lid or, when the free end of the spring member returns to the original position somehow or other, it tends to scratch off the wall surface, producing enough scrap to cause a potential problem.
In the prior art arrangement illustrated in FIG. 6 the free end of the spring member is bent and easy to slide along the underside (inner surface) of the top wall 35 of the upper casing 2. This causes a problem of frequent disengagement of the front lid from the lower casing during the course of assembling.
In the other arrangement according to FIG. 7 the tip of the free end of the spring member is allowed to bite into the upper casing so as to prevent the disengagement of the front lid. This results in changes in the spring force due to the growing bite into the casing of the free end of the spring with repeated swing of the front lid after the assembling. Also, scratch of the casing with the increasing depth of bite can produce a dropout problem.